THE STRUCTURE OF PROTOPLASM 247 



tration and high viscosity, the former was elastic and the latter 

 not; the former held a small metal particle in suspension, while 

 the latter could not support the same particle. It would seem, 

 therefore, that the elastic yet thin soap solution possessed a 

 structure that would account for its elastic qualities and for 

 its ability to support a metal particle, while the thicker yet 

 inelastic soap lacked such a structure. This supposition was 

 supported by microscopic examination. The elastic soap 

 solution contained long and slender crystals, while the other 

 soap resembled chalk dust. We have in the behavior and 



Fig. 126. — A brush heap of imaginary linear molecules. 



structure of these two soaps the basis of all generally accepted 

 hypotheses of the structure of jellies. Elastic colloidal systems 

 are buUt up of linear crystalline units. Their intermeshing gives 

 elasticity and rigidity to liquids which yet flow freely and 

 smoothly. This is structurally possible if we regard the frame- 

 work of fibers as not fixed but labile, capable of readjustment 

 and comparable to a loosely put together brush heap (Fig. 126). 

 A brush heap is elastic; a sand pile, inelastic. 



Before carrying the story of the fibrous structure of proto- 

 plasm over to cellulose, investigations on which have yielded 

 much in regard to gel structure in general, let us see how the inter- 

 meshed fibrous structure is associated with the protoplasmic 

 emulsion. Milk illustrates the situation almost perfectly. 

 Viewed through the microscope, milk is an emulsion of butterfat 

 in an aqueous medium. More than this is not visible. When 

 milk coagulates, the emulsion plays only a passive part. It is 



